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An explanation using an integrated set of principles that organizes and predicts observations.

Hypothesis

A testable prediction, often implied by a theory.

Operational definition

A statement of the procedures (operations) used to define research variables. For example, intelligence may be operationally defined as what an intelligence test measures.

Replication

Repeating the essence of a research study, usually with different participants in different situations, to see whether the basic finding extends to other participants and circumstances.

Case study

An observation technique in which one person is studied in depth in the hope of revealing universal principles.

Survey

A technique for ascertaining the self-reported attitudes or behaviors of people, usually by questioning a representative, random sample of them.

False consensus effect

The tendency to overestimate the extent to which others share our beliefs and behaviors.

Population

All the cases in a group, from which samples may be drawn for a study. (Note: except national studies, this does not refer to a country's whole population.)

Random sample

A sample that fairly represents a population because each member has an equal chance of inclusion.

Naturalistic observation

Observing and recording behavior in naturally occurring situations without trying to manipulate and control the situation.

Correlation coefficient

A statistical measure of the extent to which two factors vary together, and thus of how well either factor predicts the other.

Scatterplot

A graphed cluster of dots, each of which represents the values of two variables. The slope of the points suggests the direction of the relationship between the two variables. The amount of scatter suggests the strength of the correlation.

Illusory correlation

The perception of a relationship where none exists.

Experiment

A research method in which an investigator manipulates one or more factors (independent vairables) to observe the effect on some behavior or mental process (the dependent variable) by the random assignment of participants.

Double-blind procedure

An experimental procedure in which both the research participants and the research staff are "blind" about whether the research participants have received the treatment or a placebo. Commonly used in drug-evaluation studies.

Placebo effect

Experimental results caused by expectations alone; any effect on behavior caused by the administration of an inert substance or condition, which is assumed to be an active agent.

Experimental condition

The condition of an experiment that exposes participants to the treatment, that is, to one version of the independent variable.

Control experiment

The condition of an experiment that contrasts with the experimental condition and serves as a comparison for evaluating the effect of the treatment.

Random assignment

Assigning participants to experimental and control conditions by chance, thus minimizing preexisting differences between those assigned to the different groups.

Independent variable

The experimental factor that is manipulated; the variable whose effect is being studied.

Dependent variable

The experimental factor - in psychology, the behavior or mental process - that is being measured; the variable that may change in response to manipulations of the independent variable.

Mode

The most frequently occurring score in a distribution.

Mean

The arithmetic average of a distribution, obtained by adding the scores and then dividing by the number of scores.

Median

The middle score in a distribution; half the scores are above it and half are below it.

Range

The difference between the highest and lowest scores in a distribution.

Standard deviation

A computed measure of how much scores vary around the mean score.

Statistical significance

A statistical statement of how likely it is that an obtained result occurred by chance.

Culture

The enduring behaviors, ideas, attitudes, and traditions shared by a large group of people and transmitted from one generation to the next.